Arteriovenous access valve system and process

ABSTRACT

An arteriovenous graft system is described. The arteriovenous graft system includes an arteriovenous graft that is well suited for use during hemodialysis. In order to minimize or prevent arterial steal, at least one valve device is positioned at the arterial end of the arteriovenous graft. In one embodiment, for instance, the arteriovenous graft system includes a first valve device positioned at the arterial end and a second valve device positioned at the venous end. In one embodiment, the valve devices may include an inflatable balloon that, when inflated, constricts and closes off the arteriovenous graft. By minimizing or preventing arterial steal, other complications associated with arteriovenous grafts are also avoided. For instance, the present invention is also well suited to preventing arteriovenous graft thrombosis, eliminating dialysis needle hole bleeding, and eliminating or minimizing arteriovenous graft pseudoaneurism formation.

BACKGROUND OF THE INVENTION

The function of kidneys, which are glandular organs located in the upperabdominal cavity of vertebrates, is to filter blood and remove wasteproducts. Specifically, kidneys separate water and waste products ofmetabolism from blood and excrete them as urine through the bladder.Chronic renal failure is a disease of the kidney in which the kidneyfunction breaks down and is no longer able to filter blood and removewaste substances. Should certain toxic waste substances not be removedfrom the blood, the toxic substances may increase to lethalconcentrations within the body.

Hemodialysis is a life-sustaining treatment for patients who have renalfailure. Hemodialysis is a process whereby the patient's blood isfiltered and toxins are removed using an extracorporeal dialysismachine. For hemodialysis to be effective, large volumes of blood mustbe removed rapidly from the patient's body, passed through the dialysismachine, and returned to the patient. A number of operations have beendeveloped to provide access to the circulation system of a patient suchthat patients may be connected to the dialysis machine.

For example, the most commonly performed hemodialysis access operationis a subcutaneous placement of an arteriovenous graft, which is madefrom a biocompatible tube. The biocompatible tube can be made of, forinstance, a fluoropolymer such as polytetrafluoroethylene. One end ofthe tube is connected to an artery while the other end is connected to avein. The arteriovenous graft is typically placed either in the leg orarm of a patient.

Blood flows from the artery, through the graft and into the vein. Toconnect the patient to a dialysis machine, two large hypodermic needlesare inserted through the skin and into the graft. Blood is removed fromthe patient through one needle, circulated through the dialysis machine,and returned to the patient through the second needle. Typically,patients undergo hemodialysis approximately four hours a day, three daysa week.

Various problems, however, have been experienced with the use of anarteriovenous graft. For example, arterial steal occurs when excessiveblood flow through the arteriovenous graft “steals” blood from thedistal arterial bed. Arterial steal can prevent the proper supply ofblood from reaching the extremity of a patient.

Various other complications can also occur. For instance, the bloodflowing through the arteriovenous graft can often reach turbulent flowrates. This stream of fast moving blood then exits the arteriovenousgraft and contacts the vein connected to the graft. This collisionbetween the flow of blood and the vein may cause the development ofmyointimal hyperplasia which leads to the thickening of the vein wallsand a narrowing of the vessel. As the vein narrows, flow through thearteriovenous graft decreases and blood within the graft may ultimatelyclot.

The cessation of blood flow through the graft caused by clot formationis known as graft thrombosis. Numerous techniques and medications havebeen studied in attempts to block the development of the scar tissue.Graft thrombosis, however, continues to remain a reoccurringcomplication associated with the use of arteriovenous grafts.

In view of the above drawbacks, a need currently exists in the art foran arteriovenous graft that can prevent and minimize arterial steal andgraft thrombosis. A process for using an arteriovenous graft inminimizing arterial steal and graft thrombosis is also needed.

SUMMARY OF THE INVENTION

In general, the present invention is directed to subcutaneousarteriovenous graft systems and to processes for using the arteriovenousgraft systems in a manner that eliminates or at least reduces arterialsteal and graft thrombosis. In one embodiment, for instance, the systemincludes an arteriovenous graft having an arterial end and an oppositevenous end. The arterial end is configured to be connected to an arteryto form an arterial anastomosis, while the venous end is configured tobe connected to a vein to form a venous anastomosis.

In accordance with the present invention, the system includes at leastone valve device positioned at the arterial end of the arteriovenousgraft. In one embodiment, for instance, the valve device comprises aninflatable balloon. The inflatable balloon is positioned so as torestrict blood flow through the arteriovenous graft when inflated. Ingeneral, the valve device should be positioned at the arterial end ofthe arteriovenous graft as close as possible to the intersection of thegraft with an artery. For example, the valve device may be positioned soas to restrict blood flow through the arteriovenous graft at a locationthat is less than about 10 mm from the intersection of the arteriovenousgraft and an artery.

The inflatable balloon of the valve device may have an annular shapethat surrounds the arteriovenous graft. The inflatable balloon may alsobe a separate structure or may be integral with the arteriovenous graft.When integral with the arteriovenous graft, the arteriovenous graft mayinclude a multi-layered segment located at the arterial end. Themulti-layered segment may comprise an inner layer and an outer layer.The inner layer constricts the graft when a fluid is fed in between theinner layer and the outer layer. When having an annular shape, theballoon may be surrounded by a rigid collar that serves to assist theballoon in constricting the graft.

In order to inflate and deflate the balloon, in one embodiment, thevalve device can further include an injection port in fluidcommunication with the inflatable balloon. The injection port defines adiaphragm configured to receive a hypodermic needle for injecting fluidinto or withdrawing fluid from the balloon. Of particular advantage, theinjection port may also be subcutaneously implanted.

In an alternative embodiment, the inflatable balloon may be positionedin operative association with a piston. In this embodiment, when theballoon is inflated, the balloon forces the piston either towards oraway from the arteriovenous graft for opening or closing the valvedevice.

In addition to the use of a valve device containing an inflatableballoon, the valve device may also comprise a magnetically activatedpiston. In this embodiment, when a magnetic field is placed in closeproximity to the valve device, the piston is moved for either opening orclosing the valve device. For example, in one embodiment, placing amagnetic field in close proximity to the valve device opens the devicewhich normally remains closed.

In one particular embodiment, the magnetically activated piston may beactivated when exposed to a changing magnetic field, such as a pulsingmagnetic field. In this embodiment, the valve device may include a coilmember configured to convert a changing magnetic field into an electriccurrent. The coil member is in communication with a solenoid. Thesolenoid is configured to move the piston and open or close the valvedevice when electric current is received from the coil member.

In one embodiment, the arteriovenous graft system further includes asecond valve device positioned at the venous end of the arteriovenousgraft. The second valve device may be any suitable valve device asdescribed above. The second valve device, for instance, may be identicalto the first valve device or, alternatively, may be different.

In general, for most applications, the second valve device is notexposed or subjected to the same fluid pressures that are exerted on thefirst valve device. In this regard, the first valve device is designedto restrict or stop fluid flow at relatively high pressures. The secondvalve device, however, may be a low pressure valve device. In oneembodiment, for instance, the second valve device may be a check valvepositioned at the venous end of the arteriovenous graft. For example,the second valve device may be formed integral with the arteriovenousgraft and may be formed from a membrane that allows fluid flow from thearteriovenous graft and into an adjoining vein but prevents fluid flowfrom the vein into the arteriovenous graft.

The arteriovenous graft of the present invention is used forhemodialysis. During hemodialysis, two hypodermic needles are insertedinto the arteriovenous graft. Blood is removed from the graft using oneneedle, circulated through a dialysis machine, and returned to thearteriovenous graft through the second needle. When hemodialysis is notbeing conducted, however, the valve devices of the present invention maybe activated in order to minimize arterial steal and prevent thrombosisof the graft.

For example, in one embodiment of the present invention, when thearteriovenous graft system only includes a single valve device at thearterial end, after hemodialysis has ended, the valve device is closedthus preventing blood flow through the graft. After the valve device isclosed, a blood compatible fluid may be injected into the graft using ahypodermic needle. As used herein, a blood compatible fluid refers toany fluid that is biocompatible with the circulation system. Forexample, in one embodiment, the blood compatible fluid is a heparinizedsaline solution. The saline solution is used to flush the graft afterthe valve device is closed in order to remove blood from the graft.

In another embodiment, after hemodialysis, the valve device is partiallyclosed to a first position thereby constricting the arteriovenous graftand reducing blood flow through the graft. The patient is then monitoredover a period of time, such as days or weeks, and the valve device maybe selectively opened or closed from the first position until arterialsteal is minimized. In this embodiment, the valve device is closed anamount sufficient to reduce blood flow through the graft without slowingthe blood flow to a point where blood clots may form.

As described above, in another embodiment of the present invention, thearteriovenous graft system includes a first valve device at the arterialend and a second valve device at the venous end. In this embodiment,after hemodialysis has ended, the first valve device at the arterial endis closed thereby preventing blood flow through the graft. A hypodermicneedle then flushes the graft with a blood compatible fluid evacuatingall blood from the graft. After the graft has been flushed with theblood compatible fluid, the second valve device is then closed and thehypodermic needle is removed from the graft.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention is set forth inthe specification with reference to the following figures.

FIG. 1 is a side view with cut away portions of a human arm illustratingthe placement of an arteriovenous graft;

FIGS. 2A, 2B and 2C are perspective views of embodiments ofarteriovenous graft systems made in accordance with the presentinvention;

FIG. 3 is a perspective view of one embodiment of a valve device thatmay be used in the arteriovenous graft system of the present invention;

FIG. 4 is a perspective view of another embodiment of a valve devicethat may be used in the arteriovenous graft system of the presentinvention; and

FIG. 5 is a perspective view of still another embodiment of anarteriovenous graft system made in accordance with the presentinvention.

Repeated use of reference characters in the present specification anddrawings is intended to represent the same or analogous features of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made to the embodiments of the invention, one ormore examples of which are set forth below. Each example is provided byway of explanation of the invention, not as a limitation of theinvention. In fact, it will be apparent to those skilled in the art thatvarious modifications and variations may be made in the inventionwithout departing from the scope or spirit of the invention. Forinstance, features illustrated or described as part of one embodimentmay be used in another embodiment to yield a still further embodiment.For example, an arteriovenous graft system may include combinations ofthe valve devices described below. Thus, it is intended that the presentinvention cover such modifications and variations as come within thescope of the appended claims and their equivalents. It is to beunderstood by one of ordinary skill in the art that the presentdiscussion is a description of exemplary embodiments only, and is notintended as limiting the broader aspects of the present invention, whichbroader aspects are embodied in the exemplary construction.

In general, the present invention is directed to an implantablearteriovenous graft system that may be used in carrying out hemodialysistreatments. Although the following description will refer to thearteriovenous graft system being implanted into an arm, it should beunderstood that the system may be implanted in any suitable location ofthe body. For example, in other embodiments, the arteriovenous graftsystem may be implanted into a leg.

In addition to being well suited for carrying out hemodialysis, thearteriovenous graft system of the present invention also prevents orminimizes arterial steal and graft thrombosis. In particular, thearteriovenous graft system is designed to prevent or minimize blood flowthrough the graft when hemodialysis is not occurring.

Referring to FIG. 1, for purposes of explanation, a right arm 10 of apatient is shown. Selected arteries (shown as dotted pathways) areillustrated in conjunction with selected veins (shown as dark pathways).An arteriovenous graft 12 is shown connected at one end to an artery andat an opposite end to a vein. In particular, the arteriovenous graft 12is connected to the brachial artery 14 and to the cephalic vein 16.

The arteriovenous graft 12 is made from any suitable biocompatiblematerial. For example, in one embodiment, the graft is made from afluoropolymer, such as polytetrafluoroethylene, which is commerciallyavailable as GORTEX™ from the W. L. Gore Company.

Referring to FIGS. 2A and 2B, one embodiment of an arteriovenous graftsystem made in accordance with the present invention is shown includingan arteriovenous graft 12. As illustrated, the arteriovenous graft 12 isconnected to an artery 14 and to a vein 16. In order to carry outhemodialysis, a first hypodermic needle 18 is inserted through the skinand into the arteriovenous graft 12. Blood is removed from thearteriovenous graft 12 through the needle and into a dialysis machine20. In the dialysis machine, waste materials are removed from the blood.After circulating through the dialysis machine 20, the blood is then fedback into the arteriovenous graft 12 through a second hypodermic needle22.

In accordance with the present invention, the arteriovenous graft systemas shown in FIGS. 2A and 2B further includes at least a first valvedevice generally 24 positioned at the arterial end of the arteriovenousgraft 12. Optionally, the arteriovenous graft system can further includea second valve device generally 26 positioned at the venous end of thearteriovenous graft. The valve devices 24 and 26 are in an open positionduring normal hemodialysis as shown in FIG. 2A. When hemodialysis hasended, however, the valve devices 24 and 26 are moved to a closedposition in order to prevent blood flow through the arteriovenous graft.In this manner, arterial steal is either eliminated or reduced. Further,by reducing arterial steal, graft thrombosis is also prevented.

In addition to minimizing arterial steal and preventing graftthrombosis, the system and the process of the present invention alsooffer various other advantages. For example, reducing or stopping bloodflow through the arteriovenous graft when hemodialysis is not occurringalso prevents the graft from bleeding when the hypodermic needles usedto carry out hemodialysis are removed from the graft. Hypodermic needlesas shown in FIG. 2B, for instance, usually have a relatively largediameter or gauge. Thus, when the needles are removed from a graft,bleeding can occur where the needles have previously been. Needle holebleeding through the graft can result in the formation of scar tissueand graft pseudoaneurisms. These complications, however, may beprevented through the use of the system of the present invention.

In the embodiment shown in FIG. 2A, the valve devices 26 and 24 eachinclude an inflatable balloon 28 and 30. When inflated, the balloons 28and 30 constrict the arteriovenous graft 12 for reducing or eliminatingblood flow through the graft.

As shown in FIG. 2A, the inflatable balloons 28 and 30, in thisembodiment, have an annular shape that surround the arteriovenous graft12. As shown, each of the inflatable balloons 28 and 30 are alsosurrounded by a rigid collar 32 and 34. Each collar 32 and 34 may beincluded in the system in order to maintain each of the balloons 28 and30 in the proper position. Further, the collars 32 and 34 also serve tobias the balloon towards the arteriovenous graft 12 when inflated. Eachcollar 32 and 34 may be made from any rigid biocompatible material. Forexample, the collars 32 and 34 may be made from a metal, such astitanium, or a plastic material.

Each annular balloon 28 and 30 may be a separate structure from thearteriovenous graft 12 or may be integral with the graft. When integralwith the graft, for instance, the graft may include a multi-layeredsegment where each of the valve devices is to be located. For example,within the multi-layered segment, the arteriovenous graft 12 may includean outer rigid layer and an inner luminal layer. The balloon 28 and 30may be formed in between the outer layer and the inner layer. Inparticular, when a fluid is injected in between the inner and outerlayers, the inner layer may expand and constrict the lumen. See FIG. 2C.

In addition to having an annular shape, it should be understood thateach balloon 28 and 30 may have any shape sufficient to constrict thearteriovenous graft when inflated. For instance, in another embodiment,each balloon 28 and 30 may be located on one side of the graft 12. Wheninflated, the balloons 28 and 30 force opposite sides of the grafttogether.

In order to inflate the balloons 28 and 30, in one embodiment as shownin FIGS. 2A and 2B, each valve device may further include an injectionport 36 and 38. For example, as shown in FIG. 2A, injection port 36 maybe in fluid communication with the balloon 28 via a tubing 40.Similarly, injection port 38 may be in fluid communication with theballoon 30 via a tubing 42. Each injection port 36 and 38 may beconfigured to be subcutaneously implanted in a patient.

In the embodiment illustrated in FIG. 2A, injection ports 36 and 38 eachinclude a diaphragm 44 and 46 positioned on one side of a housing 48 and50. The housings 48 and 50 may be made from any suitable rigid andbiocompatible material. For example, each housing may be made from ametal, such as titanium. Each diaphragm 44 and 46, on the other hand,may be made from a material capable of receiving the tip of a hypodermicneedle. For example, each diaphragm 44 and 46 may be made from anelastomeric film, such as a silicone membrane.

As shown particularly in FIG. 2B, in order to inflate or deflate theballoons 28 and 30, hypodermic needles 52 and 54 may inject a fluid intoeach of the injection ports 36 and 38 through the diaphragms 44 and 46.The fluid travels from the injection ports 36 and 38 through the tubing40 and 42 and into each respective balloon 28 and 30. Similarly, thehypodermic needles 52 and 54 may also be used to withdraw fluid from theballoons 28 and 30.

As shown in FIG. 2B, once inflated, the balloons 28 and 30 constrict thearteriovenous graft 12 at the arterial end and at the venous end. Thefluid used to inflate the balloons 28 and 30 may vary depending upon theparticular application. The fluid may be, for instance, a gas or liquid.In one embodiment, for instance, a saline solution may be injected intothe injection ports 36 and 38 for inflating the balloons. In oneembodiment, it may take from about 2 ccs to about 6 ccs of fluid totransition each balloon valve 28 and 30 from an open position to aclosed position.

When closed, each valve device should be capable of maintaining itsposition when exposed to systolic pressure. For example, systolicpressures in arteries may be greater than about 250 mmHg, such as fromabout 170 mmHg to about 270 mmHg.

In addition to withstanding relatively high fluid pressures, each of thevalve devices 24 and 26 should also be constructed so that the valvedevices can constrict the arteriovenous graft as close as possible tothe intersection of the graft with the artery 14 and the vein 16. Forexample, the first valve device 24, in one embodiment, constricts thearteriovenous graft at a distance of from about 5 mm from the arterialanastomosis, such as no greater than about 20 mm from the arterialanastomosis. The position of the second valve device 26 in relation tothe venous anastomosis may also be within the above defined limits.

The methods for using the a rteriovenous graft system of the presentinvention will now be discussed in relation to a system that contains asingle valve device positioned at the arterial end of the graft and asystem that contains two valve devices as shown in FIGS. 2A and 2B.

When the arteriovenous graft system of the present invention contains asingle valve device positioned at the arterial end, in one embodiment,the valve device may be positioned so as to constrict blood flow throughthe graft when hemodialysis is not occurring. In this embodiment,arterial steal is not being completely prevented but is being minimized.In particular, the single valve device constricts the graft so thatblood flow through the graft continues without clotting but is at areduced flow rate.

In this embodiment, the patient's condition may need to be monitoredover a period of time, such as days or weeks, and the valve device maybe adjusted in order to minimize arterial steal without causing acomplete blood stoppage. For instance, over several days or weeks, thearteriovenous graft of the patient may be monitored and the valve devicemay be adjusted so as to gradually increase or decrease the narrowing ofthe arteriovenous graft. The ultimate position of the valve will varydepending upon the patient and the location of the arteriovenous graft.

In an alternative embodiment, the single valve device may be used tocompletely close off the arteriovenous graft 12 at the arterial end. Inthis embodiment, during hemodialysis, the valve device 24 is in the openposition and the arteriovenous graft 12 is cannulated with the twodialysis needles 18 and 22 as shown in FIG. 2A. Upon completion ofdialysis, a fluid is injected into the injection port 36 of the firstvalve device causing the balloon 28 to inflate thereby closing the valvedevice and eliminating arterial blood flow through the graft.

After the valve device is closed, a blood compatible fluid is theninjected into the arteriovenous graft 12 through, for instance, adialysis needle to flush any residual blood out of the graft. The bloodcompatible fluid can be, for instance, heparinized saline. The residualblood is flushed out of the graft in order to prevent any clotting.

In this embodiment, some residual saline remains in the graft untilhemodialysis is once again conducted on the patient. This embodimentshould only be used when it is determined that substantially no bloodfrom the vein 16 will flow into the graft once valve device 24 isclosed.

In order to prevent any blood flowing from the vein 16 back into thearteriovenous graft 12 after the first valve device 24 has been closed,in one embodiment of the present invention as shown particularly inFIGS. 2A and 2B, the arteriovenous graft system can include the secondvalve device 26. In this embodiment, the process as described above isrepeated. After the arteriovenous graft 12 is flushed with a bloodcompatible fluid, however, a fluid is injected into the injection port38 of the second valve device 26 which causes the second valve device toclose.

In addition to the valve devices as illustrated in FIGS. 2A and 2B, inother embodiments, other valve devices may also be utilized in thesystem of the present invention. For example, referring to FIG. 4,another embodiment of a valve device generally 60 is shown incommunication with an arteriovenous graft 12. In this embodiment, thevalve device 60 includes a fluid chamber 62 in communication with aninjection port 64 similar to the injection ports described above. Asshown, injection port 64 includes a diaphragm 68 configured to receivefluid from a hypodermic needle 70.

The valve device 60 further includes a piston 72 contained within ahousing 74. The piston 72 is positioned below the fluid chamber 62.

In this embodiment, when a fluid is injected from the needle 70 into theinjection port 64, the fluid is forced into the fluid chamber 62 via atube 66. The pressure of the fluid then forces the piston 72 to lowerclosing the valve and constricting flow through the arteriovenous graft12.

Valve device 60 as shown in FIG. 4 may be used in a single valve systemof the present invention or in a double valve system of the presentinvention as illustrated in FIG. 2A.

Referring to FIG. 3, another embodiment of a valve device generally 80that may be used in the arteriovenous graft system of the presentinvention is illustrated. In this embodiment, the valve device 80includes a housing 82 containing a magnetically actuated piston 84.Specifically, the valve device is configured such that the piston 84moves between an open and closed position when the valve device iscontacted with a magnetic field.

In this particular embodiment, the valve device 80 includes a coilmember 86. The coil member 86 is configured to convert a pulsatingmagnetic field into an electric current. As shown, the coil member 86then supplies the electric current to a solenoid 88. Solenoid 88 thenmoves the piston 84 to either open or close the valve device.

In order to activate the valve device 80, a magnetic key 90 is placedclose to the skin of a patient. In this embodiment, the magnetic key 90may be an electromagnet that creates a pulsating magnetic field. Asdescribed above, the pulsating magnetic field is then converted into anelectric current by the coil member 86. The magnetic key 90 may beconfigured either to open or to close the valve device. In oneembodiment, for instance, the valve device 80 may normally be found in aclosed position blocking off the arteriovenous graft 12. When themagnetic key 90, however, is placed adjacent to the patient's skin, thevalve device 80 then opens allowing blood to circulate through thegraft. In other embodiments, however, it should be understood that thevalve device may be configured to close when placed adjacent to themagnetic key 90.

In addition to the valve device 80 as shown in FIG. 3, othermagnetically activated valves may be used in the system of the presentinvention. For example, in another embodiment of the present invention,the valve device may include a piston in operative association with apermanent magnet. A ferrous plate may be positioned on the opposite sideof the arteriovenous graft. Thus, the permanent magnet contained in thepiston is attracted to the ferrous surface for closing off thearteriovenous graft. When a magnet with opposite polarity, however, isplaced adjacent to the valve device, the permanent magnet containedwithin the piston is attracted to the reverse magnetic field causing thevalve to open.

Referring to FIG. 5, another embodiment of an arteriovenous graft systemmade in accordance with the present invention is shown. Like referencenumerals have been used in order to identify similar features andelements of other embodiments. As shown, in this embodiment, thearteriovenous graft system includes a first valve device generally 24 atthe arterial end of the graft similar to the valve device shown in FIGS.2A and 2B. In particular, the first valve device 24 includes a balloon28 that is inflated or deflated using an injection port 36. The balloon28 is for constricting the arteriovenous graft when desired. Asexplained above, the first valve device 24, for most applications, iscapable of maintaining a closed or constricted position on the grafteven when exposed to relatively high fluid pressures. In someembodiments, however, these same pressures are not experienced at thevenous end of the graft.

In this regard, in this embodiment, the arteriovenous graft 12 includesa second valve device generally 100 that may be described as a lowpressure valve device when compared to the first valve device 24.

For example, in one embodiment, the second valve device 100 may be acheck valve that allows fluid flow from the graft 12 into the vein 16but does not permit flow from the vein 16 into the graft 12. In general,any suitable check valve may be used in, accordance with the presentinvention.

In the embodiment shown in FIG. 5, the second valve device 100 includesa membrane 102 made from, for instance, a polymeric film that is formedor is connected so as to be integral with the arteriovenous graft 12.The membrane 102 may be, for instance, a flap that allows fluid flow inone direction from the graft 12 into the vein 16. The membrane 102 maybe formed from a single piece of film or may be formed from multiplesegments. For example, in one embodiment, the film can include one ormore slits that permit fluid flow in one direction.

The arteriovenous graft system in FIG. 5 provides various advantages.For example, in the embodiment shown in FIG. 5, only the first valvedevice 24 needs to be manually opened or closed.

In the embodiment shown in FIG. 5, the first valve device is representedas a balloon valve. It should be understood, however, that the firstvalve device may be any of the other valve devices shown and describedabove.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

1. A subcutaneous arteriovenous graft system comprising: anarteriovenous graft having an arterial end and an opposite venous end;and at least one valve device positioned at the arterial end of thearteriovenous graft, the valve device comprising an inflatable balloonin communication with the arteriovenous graft, the valve device having aclosed position when the inflatable balloon is inflated and wherein,when the valve device is in the closed position, blood flow through thearteriovenous graft is prevented in order to minimize arterial steal. 2.A system as defined in claim 1, further comprising a second valve devicepositioned at the venous end of the arteriovenous graft, the secondvalve device also comprising an inflatable balloon, wherein the firstvalve device and the second valve device substantially prevent bloodflow through the arteriovenous graft when the respective balloons areinflated.
 3. A system as defined in claim 2, wherein the inflatableballon of the first valve device and the inflatable balloon of thesecond valve device have an annular shape that surrounds thearteriovenous graft.
 4. A system as defined in claim 3, wherein eachvalve further comprises an outer collar surrounding each respectiveinflatable balloon.
 5. A system as defined in claim 2, wherein the firstvalve device is capable of preventing blood flow when exposed tosystolic arterial pressure in between about 170 mmHg to about 270 mmHg.6. A system as defined in claim 2, wherein each of the valve devicesfurther comprise an injection port in fluid communication with each ofthe inflatable balloons, each of the injection ports defining adiaphragm configured to receive a hypodermic needle for injecting orwithdrawing fluid from each respective balloon.
 7. A system as definedin claim 1, further comprising a second valve device positioned at thevenous end of the arteriovenous graft, the second valve devicecomprising a check valve.
 8. A system as defined in claim 7, wherein thecheck valve comprises a membrane positioned within the arteriovenousgraft.
 9. A system as defined in claim 8, wherein the membrane includesa slit that only allows fluid flow in one direction.
 10. A system asdefined in claim 8, wherein the membrane comprises a moveable flap thatonly allows fluid flow in one direction.
 11. A system as defined inclaim 7, wherein the check valve only permits fluid flow out of thearteriovenous graft through the venous end.
 12. A system as defined inclaim 1, further comprising an injection port in fluid communicationwith the inflatable balloon, the injection port defining a diaphragmconfigured to receive a hypodermic needle for injecting or withdrawingfluid from the balloon.
 13. A system as defined in claim 12, wherein theinjection port comprises a metal housing, the diaphragm being located onone surface of the housing.
 14. A system as defined in claim 1, whereinthe arteriovenous graft is made from a material comprising afluoropolymer.
 15. A system as defined in claim 1, wherein the valvedevice is positioned at a location that is less than about 20 mm fromthe intersection of the arteriovenous graft and an artery.
 16. A systemas defined in claim 1, wherein the inflatable balloon comprises amulti-layered segment located at the arterial end of the arteriovenousgraft, the multi-layered segment comprising an inner layer and an outerlayer, the inner layer constricting flow through the arteriovenous graftwhen a fluid is fed in between the inner layer and the outer layer. 17.A system as defined in claim 1, wherein the inflatable balloon ispositioned in operative association with a piston, wherein, wheninflated, the balloon forces the piston against the arteriovenous graftfor constricting same.
 18. A system as defined in claim 1, wherein theinflatable balloon is made from a material comprising silicone.
 19. Asystem as defined in claim 1, wherein the inflatable balloon constrictsthe arteriovenous graft when inflated with from about 2 ccs to about 6ccs of fluid.
 20. A subcutaneous arteriovenous graft system comprising:an arteriovenous graft having an arterial end and an opposite venousend; a first valve device positioned at the arterial end of thearteriovenous graft, the valve device comprising an inflatable balloon,the inflatable balloon being positioned so as to prevent blood flowthrough the arteriovenous graft when inflated, the inflatable balloonbeing in communication with a first injection port, the injection portdefining a diaphragm configured to receive a hypodermic needle forinjecting or withdrawing fluid from the balloon, the injection portbeing configured to be implanted subcutaneously; a second valve devicepositioned at the venous end of the arteriovenous graft, the secondvalve device comprising an inflatable balloon, the inflatable balloonbeing positioned so as to prevent blood flow through the arteriovenousgraft when inflated, the inflatable balloon being in communication witha second injection port, the second injection port defining a diaphragmconfigured to receive a hypodermic needle for injecting or withdrawingfluid from the inflatable balloon, the second injection port also beingconfigured to be implanted subcutaneously.
 21. A system as defined inclaim 20, wherein the first valve device is positioned at a locationthat is less than about 20 mm from the intersection of the arteriovenousgraft and an artery and wherein the second valve device is positionedgraft at a location that is less than about 20 mm from the intersectionof the arteriovenous graft and a vein.
 22. A system as defined in claim20, wherein the inflatable balloon of the first valve device and theinflatable balloon of the second valve device have an annular shape thatsurrounds the arteriovenous graft, each of the inflatable balloons beingsurrounded by an outer collar.
 23. A process for reducing arterial stealand graft thrombosis in an arteriovenous graft comprising: providing anarteriovenous graft having been subcutaneously implanted in a patient,the arteriovenous graft including an arterial end in fluid communicationwith an artery and a venous end in fluid communication with a vein, thearteriovenous graft further comprising at least one valve devicepositioned at the arterial end of the graft; closing the first valvedevice at the arterial end of the arteriovenous graft and therebystopping blood flow through the arteriovenous graft; injecting into thearteriovenous graft through a hypodermic needle a blood compatible fluidfor flushing the arteriovenous graft and evacuating blood from thegraft; removing the hypodermic needle from the arteriovenous graft. 24.A process as defined in claim 23, wherein the arteriovenous graftfurther comprises a second valve device positioned at the venous end ofthe graft and wherein the process further comprises the step of closingthe second valve device after the arteriovenous graft has been flushedwith the blood compatible fluid.
 25. A process as defined in claim 24,wherein the first valve device and the second valve device both includean inflatable balloon, the inflatable balloon being positioned so as torestrict blood flow through the arteriovenous graft when inflated.
 26. Aprocess as defined in claim 25, wherein the inflatable balloon of thefirst valve device and the inflatable balloon of the second valve devicehave an annular shape that surrounds the arteriovenous graft.
 27. Aprocess as defined in claim 26, wherein the first valve device and thesecond valve device each further comprise an outer collar surroundingeach respective inflatable balloon.
 28. A process as defined in claim25, wherein the first valve device and the second valve device eachfurther comprise an injection port in fluid communication with eachrespective inflatable balloon, each injection port defining a diaphragmconfigured to receive a hypodermic needle for injecting or withdrawingfluid from each respective balloon.
 29. A process as defined in claim24, wherein the first valve device and the second valve device eachcomprise a magnetically activated piston, wherein, when a magnetic fieldis placed in close proximity to each valve device, each respectivepiston is moved for opening or closing the valve device.
 30. A processas defined in claim 29, wherein the first valve device and the secondvalve device each open or close when exposed to a changing magneticfield, each valve device further comprising a coil member configured toconvert a changing magnetic field into an electric current, the coilmember being in communication with a solenoid, the solenoid beingconfigured to move each respective piston and open or close eachrespective valve device when an electric current is received from therespective coil member.
 31. A process as defined in claim 24, whereinthe first valve device is positioned so as to restrict blood flowthrough the arteriovenous graft at a location that is less than about 20mm from the intersection of the arteriovenous graft and the artery andwherein the second valve device is positioned so as to restrict bloodflow through the arteriovenous graft at a location that is less thanabout 20 mm from the intersection of the arteriovenous graft and thevein.
 32. A process as defined in claim 24, wherein the first valvedevice and the second valve device each comprise a piston incommunication with a fluid chamber, wherein, when a fluid is forced intoeach respective fluid chamber, each respective piston closes which inturn constricts the arteriovenous graft.
 33. A process as defined inclaim 24, wherein the second valve device comprises a check valve.
 34. Aprocess as defined in claim 23, wherein the blood compatible fluidcomprises a saline solution.
 35. A subcutaneous arteriovenous graftsystem comprising: an arteriovenous graft having an arterial end and anopposite venous end; a first valve device positioned at the arterial endof the arteriovenous graft, the first valve device including a closedposition that prevents blood flow through the arteriovenous graft; and asecond valve device positioned at the venous end of the arteriovenousgraft, the second valve device comprising a check valve.
 36. A system asdefined in claim 35, wherein the first valve device comprises a fluidactuated valve or a magnetically actuated valve.
 37. A system as definedin claim 35, wherein the check valve comprises a membrane located withinthe arteriovenous graft, the membrane only allowing fluid flow outthrough the venous end of the graft.